Hello Amiry,
I know both products and can tell you with good conscience that the sound quality is good with both, but the Arc offers a better listening experience, especially for films that support modern sound standards. It's also a lot bigger than the Beam.

We have Arc in combination with Sub and two One in use, which sounds quite powerful. We didn't have the Beam, but a Samsung soundbar with subwoofer, etc., which also sounded OK. Arc is very heavy and massive in construction. When you unpack it, you are already looking forward to it. But the sub certainly makes the difference.